Conventionally, for the purpose of preventing water in the water pipe valve from freezing in winter season at cold districts, it has been proposed a device, in which a water pipe valve was controlled so as to be slightly opened in order to flow a water continuously at a little amount, which is comparatively warm because of being flown from the duct under the ground.
The valve designed for performing this above-mentioned operation was disclosed in the Japanese Unexamined Gazette of the Patent Application No. 60-223542. However, this valve as above has to be complicated structures, in which a screw stopper for the water pipe valve was entirely remodelled newly to be provided with a spring made of shape-memory alloy.
So, for the purpose of accomodating a screw stopper as above, it must be large in size and bulky. It was a problem to exchange a screw stopper and/or a water pipe valve for especially prepared larger and complicated one. This fact leads to the defect of high cost in their construction.